1. Field of the Invention
The present invention generally relates to a high temperature superconducting step-edge Josephson junction and its fabricating method and, more particularly, to a step-edge junction using a copper oxide high-temperature superconductor thin film and its fabricating method.
2. Description of the Related Art
In a case where a step-edge junction is fabricated by depositing a superconductor thin film at a step edge that is previously formed on a single crystalline substrate, a portion of the thin film grown on an inclined surface of the step edge has a different crystal orientation from a portion of the thin film grown on the portions above and below the step. As a result, grain boundaries are formed in the upper and lower portions of the inclined surface of the step edge.
In fabrication of the step-edge Josephson junction, the most important thing is to prepare highly inclined and linear steps with good reproducibility on a single crystalline substrate.
Therefore, in the prior art, many substances have been proposed for an ion-milling mask to be used in the fabrication of steps, including Nb (See. K. P. Daly et al., Applied Physic Letters, Vol. 58(5), pp 543-545 (1991)), diamond-like carbon (DLC) (See. J. Z. Sun et al., Applied Physics Letters, Vol. 63(11), pp 1561-1563 (1993)) and amorphous carbon thin film (See. H. R. Yi et al., Applied Physic Letters, Vol. 65(9), pp 1177-1179 (1994), etc.
Alternatively, the step edge to be used for fabrication of a step-edge junction on a single substrate can be prepared by a method using NaCl and CaO thin films (See. Subura Tanaka et al., U.S. Pat. No. 5,525,582 (1997)) or using a PrBa2Cu3O7xe2x88x92x (PBCO) thin film (See. Takao Nakamura et al., U.S. Pat. No. 5,721,196 (1998)).
However, there still remains a problem involving a low reproducibility because the related art step edge is fabricated using a separate ion-milling mask or by a complicated process of fabrication.
It is therefore an object of the present invention to provide a method for fabricating a high temperature superconducting step-edge junction with good reproducibility for use purpose as the high-speed and high-frequency devices for communications.
To achieve the above object, there is provided a method for fabricating a high temperature superconducting step-edge Josephson junction including the steps of: (i) preparing a step-edge on a substrate; (ii) depositing a metal thin film on the step-edge substrate obtained; and (iii) forming a micro-bridge pattern on the deposited metal thin film by photolithography and ion milling and then performing a heat treatment.